1. Field of the Invention
The present invention relates to a phase-change type optical information recording medium, more specifically an optical information recording medium which can record, read, and overwrite the information by utilizing the phase transition characteristics of the recording layer thereof.
2. Discussion of Background
There is conventionally known a phase-change type optical information recording medium as one of the optical memory media which can record, read and erase information by means of the irradiation of electromagnetic wave, in particular, laser beam. The phase-change type optical recording medium has the capabilities to record, read and erase information by utilizing the phase transition of a recording layer thereof, for example, from a crystalline phase to an amorphous phase, or from a crystalline phase to a crystalline phase. The above-mentioned phase-change type optical information recording medium has the advantages in that it makes it possible to overwrite the information by the irradiation of a single beam, which is considered to be difficult for the conventional magnetoptic memory media, and the optical system of a driving device for the recording medium becomes simple. Therefore, the research and development has been recently conducted in the field of such a phase-change type optical information recording medium.
As disclosed in U.S. Pat. No. 3,530,441, chalcogen type alloy materials for the recording medium such as Ge-Te, Ge-Te-Sb, Ge-Te-S, Ge-Se-S, Ge-Se-Sb, Ge-As-Se, In-Te, Se-Te and Se-As are conventionally employed. Further, for the purpose of improving the stability of the recording medium and accelerating the crystallization of the recording layer thereof, there are proposed more improved materials, for example, Ge-Te-Au in the Japanese Laid-Open Patent Application 61-219892, Ge-Te-Sn-Au in the Japanese Laid-Open Patent Application 61-270190 and Ge-Te-Pd in the Japanese Laid-Open Patent Application 62-19490. In addition, there is proposed a material of Ge-Te-Se-Sb with a specific elemental composition ratio in the Japanese Laid-Open Patent Application 62-73438 to maintain the performance of the recording medium after the recording and erasing operation are repeated.
However, the above-mentioned conventional phase-change type optical information recording media do not satisfy all the requirements. There is demanded a phase-change type optical information recording medium, in particular, with excellent recording and erasing sensitivity, which can completely erase the previous information in the course of the overwrite operation to keep the erasing ratio, and has a long life of recorded and not recorded areas thereof.